Project Summary A recent international workshop convened to review the findings from asthma/allergy birth cohorts and identify knowledge gaps and research priorities. In their summary, they conclude that a key research priority need is to better understand the mechanisms of progression to asthma in early childhood. This proposal will help to fill this critical gap in understanding. Thymic stromal lymphopoietin (TSLP) is a major epithelial cytokine that and is strongly implicated in the pathogenesis of AD, allergic sensitization, and asthma. Antigen exposure in the skin in the context of TSLP is sufficient to induce AD and airway inflammation in the lung, suggesting that skin-derived TSLP is sufficient to drive the progression of AD to asthma. TSLP single nucleotide polymorphisms (SNPs) have been associated with allergic sensitization and asthma, as well as AD. Expression of TSLP is increased in AD and disease-associated eQTL in TSLP correlate with TSLP expression. These studies collectively suggest TSLP promotes allergic sensitization and AD in early life and may be an important driver of progression of a subset of early allergic phenotypes to asthma. Despite the increasingly evident role of TSLP in allergic disease, the mechanisms by which TSLP is induced in human skin remain unclear. We recently found that among the known TSLP SNPs, 25% disrupt or create a new CpG site, which is significantly higher than the frequency of CpG- SNPs across the genome, and the prevalence of CpG-SNPs is even higher among TSLP SNPs that have been associated with allergic disorders. We have recently identified candidate enhancers upstream of the TSLP locus that may drive TSLP expression and found that allergic disease-associated TSLP SNPs, including eQTL, reside or are in strong linkage disequilibrium with these candidate enhancers. Based on our preliminary data, we hypothesize that mechanical stress and/or barrier dysfunction are translated to TSLP expression through dedicated enhancers and that genetic variation in the TSLP locus relaxes this regulation resulting in enhanced TSLP expression and clinical progression to asthma. This application will have significant public health impact. Through the proposed aims, we will (1) elucidate the mechanisms by which barrier defects in human epidermal keratinocytes are sensed and translated to TSLP transcription; (2) delineate the impact of known risk and protective alleles on this regulation; (3) determine the utility of genetic and epigenetic variation in the TSLP locus as biomarkers of disease progression to asthma; and (4) provide the foundation for development of new algorithms to accurately predict the development of asthma among preschool aged children.